Fire doors, as used in residential, commercial, and industrial applications, are typically employed in conjunction with fire walls to provide fire protection between different zones of a structure, and particularly to isolate high fire risk areas of a building from the remainder of the structure, such as the garage from the living quarters of a dwelling. Fire doors may be constructed in both panel or flush-type configurations. They often include facings on the two major planar surfaces and a core which may be solid or include some hollow space. Edge banding is often provided around the door periphery for structural reasons.
Fire doors usually are not capable of indefinitely withstanding the high temperature conditions of a fire, but rather, are designed to maintain the integrity of the fire wall for a limited time to permit the occupants of a building to escape and to delay the spread of the fire until fire control equipment can be brought to the scene. Various tests have been devised for determining the reliability of fire doors which are based, in part, on such factors as the time that a given door can withstand a certain temperature while maintaining its integrity. One such test is the ASTM E-152 fire test, which requires a door to maintain its integrity for periods ranging up to 1.5 hours while withstanding progressively higher temperatures within the range of 1750.degree. F. to 1800.degree. F. and the erosive effects of a high pressure fire hose at the conclusion of the fire exposure.
Considerations in fire door design, in addition to retarding the advance of a fire, include the cost of raw materials and the cost of fabrication. Furthermore, the weight of the door is important, both from the standpoint of ease in handling and the cost of transportation. The strength of the door is also a significant factor, since fire doors must pass the previously noted fire and water stream test as well as have the requisite structural strength to withstand normal use and abuse. Finally, fire doors must provide support and split-resistance in localized areas where hinges, knobs, and locks are mounted.
Fire-resistant doors have, in the past, been made in a variety of constructions utilizing a number of different materials, including wood, metal and mineral materials. Early forms of fire doors simply consisted of wooden cores faced with metal sheeting. Although wood in ample thicknesses is an effective fire and heat retardant, doors of this construction tend to be heavy and are expensive to fabricate and transport.
It has also been proposed to make fire doors having a core comprising particles of expanded perlite which are bound together with one or more binders including gypsum, cement and inorganic adhesive material. In order to provide sufficient strength, particularly to withstand handling of the core during manufacture, the core is compressed to compact the mixture to a relatively high density, resulting in a heavy door.
Other fire doors have included conventional gypsum wallboard panels as a core material. However, conventional wallboard does not have sufficient structural integrity to withstand a 90 minute fire and hose stream test and would therefore be unsuitable in many fire door applications. Furthermore, because of the lack of appreciable flexural strength, internal wooden structural members such as rails or mullions have been found necessary to support and strengthen wallboard panels. The need for such reinforcing elements increases the cost of materials and assembly of such doors.
The art has been replete with numerous examples of fire door constructions, some of which have been commercially exploited. See Greve and Richards, U.S. Pat. No. 4,159,302, ('302), issued Jun. 26, 1979; Lehnert et al., U.S. Pat. No. 4,811,538, ('538), issued Mar. 14, 1989; and Lehnert et al., U.S. Pat. No. 4,748,771, ('771), issued Jun. 7, 1988, all of which are hereby incorporated by reference.
Greve and Richards '302 discloses a set gypsum-containing composition which is especially useful as a core in a solid core fire door. Lehnert '538 describes a fire door capable of withstanding a 20 minute ASTM E-152 fire test and which is partially hollow but has a core of set gypsum faced with fibrous mats. Lehnert '771 discloses set gypsum-containing edge banding for use in fire doors for obtaining a successful 90 minute ASTM E-152 fire rating. This edge banding system contains a laminated tripartite construction which includes an inner strip comprising a cast gypsum mixture, an intermediate fiber-reinforced plastic strip, and an outer strip of natural wood. This edge banding is surprisingly complex and correspondingly expensive. The complexity is necessary, at least in part, because the combination of the gypsum and wood strips alone does not provide the screw-holding capacity required for hinges, latch mechanism, etc. The thin plastic strip is therefore necessary to provide structural support for these attachments The gypsum strip included in this edge banding construction includes gypsum, glass fiber, raw vermiculite, and clay, together with a small amount of paper fiber (less than 2% by weight), wood chips, and a resin binder, which may be polyvinyl acetate.
While in the main, commercial fire-resistant materials are known to possess certain mechanical and fire-resistant properties which are acceptable in fire doors, they often require expensive, cumbersome, or potentially hazardous additives to achieve those properties. Thus, there is a need for a composition and structure which includes safe and inexpensive components from which superior fire doors and panels can be made.